1. Field of the Invention
The present invention relates to a multiple-wire wound helical antenna which is used mainly for a mobile radio device such as a portable telephone.
2. Related Art of the Invention
The recent years have seen a rapid development of mobile telecommunication such as portable telephones, and as a result, not only portable telephone systems using ground stations are wanted but systems using satellites as well are expected. Meanwhile, an antenna is one of important devices of a portable telephone terminal.
In the following, an example of a conventional quadrifilar helical antenna mentioned above will be described with reference to an associated drawing.
FIG. 9 is a block diagram showing a conventional quadrifilar helical antenna. In FIG. 9, denoted at 201 is a quadrifilar helical antenna radiant section, denoted at 202 is a 3 dB hybrid, and denoted at 203 is an input/output terminal. An operation of the quadrifilar helical antenna having such a structure will be described below.
The quadrifilar helical antenna 201, when dimensioned to have an appropriate size and fed at the input/output terminal 203 through the 3dB hybrid 202, exhibits radiation pattern having a conical beam characteristic as that shown in FIG. 10.
However, since the directivity is always upward with such a structure described above, if this antenna is disposed to a portable telephone which utilizes a satellite, the directivity becomes downward with the antenna folded during stand-by, whereby a radio wave from above is failed to be received.